There are others on this site that are more tolerant of your "low pressure", "to at least", "a certain gas" BS, but I have lost patience. If you want an Engineering answer then you need to provide Engineering Data. The "certain gas" really angers me. If you're not willing to disclose the gas species, then how would any of the helpful people on this site know if they need to consider corrosive gas, poisonous gas, or gas near a phase boundary (all have a definite impact on compressor selection). Is your "low pressure" above or below atmospheric? It kind of matters.
If this project is Oh So Confidential, then stop trying to get free Engineering and hire someone who can tell a compressor from a bicycle and have them sign an NDA.
David